As is well known, in a variety of electrical or electronic devices (systems) having a radio communication function, the waveguide tube slot antenna is used as an antenna for transmitting or receiving a radio wave having a high-frequency bandwidth (for example, radio wave having a millimeter wave band) and a radio wave having a low-frequency bandwidth (for example, radio wave having a centimeter wave band). The radio wave having a millimeter wave band is used, for example, for an on-vehicle radar system, and the radio wave having a centimeter wave band is used, for example, for a satellite broadcasting system using a broadcasting satellite (BS), a communication satellite (CS), or the like, a data transmission system such as a wireless LAN or Bluetooth (trademark), and an electronic toll collection system which is abbreviated to ETC (trademark). The radio wave having a millimeter wave band represents a radio wave having a wavelength of from to 10 mm and a frequency of from 30 GHz to 300 GHz, and the radio wave having a centimeter wave band represents a radio wave having a wavelength of from 10 mm to 100 mm and a frequency of 3 GHz to 30 GEL.
The need has arisen for reducing the cost of the waveguide tube slot antenna so as to promote lower prices for the variety of systems having the radio communication function. Accordingly, the applicant of the present application has proposed a waveguide tube slot antenna made of a resin in Patent Literature 1 described below. More specifically, the applicant has proposed a waveguide tube slot antenna that includes: a waveguide tube that is made of a resin and includes a waveguide extending in a tube axis direction, with a defining surface of the waveguide covered with a conductive coating film; and a plurality of radiating slots provided at predetermined intervals along the tube axis direction of the wave guide, the waveguide tube including a first waveguide tube forming member and a second waveguide tube forming member each having a transverse section having a shape with an end (a cross section orthogonal to the tube axis direction) and being configured to define the waveguide by being coupled to each other.